This month, San Francisco is launching an innovative program designed to catch new HIV infections shortly after they occur - when the risk of transmission is the highest.

The goal of the two-year pilot project, the first of its kind in the nation, is to reduce by half the number of new HIV cases.

During the two- or three-month period after infection, the viral load is highest and the danger of transmission is also at its peak. As many as half of all new infections are estimated to occur during the acute phase.

"The virus gets in your body and starts to replicate at a very high rate before the natural immune responses of your body start to mobilize," said Mark Cloutier, chief executive of the San Francisco AIDS Foundation.

The expanded testing, along with counseling, will take place at Magnet, a community health center for gay men in the Castro.

Clients who report engaging in recent, high-risk behavior will be invited to take viral RNA (ribonucleic acid) testing, which will identify those who are acutely infected. They will also be encouraged to alert their partners.

It takes two weeks to get results. During that time, said Steve Gibson, director of Magnet, clients are counseled to behave prudently, as if they were HIV-positive.

Tough populations

Testing will also be expanded elsewhere in the city, including the Tenderloin. One of the goals is to reach a segment of society that has been difficult to reach.

"We're hoping to identify African American men who are having sex with other men," Cloutier said. "The house is on fire for African American men who have sex with other men."

The virus has shown a startling prevalence in young black men. A report in September by the federal Centers for Disease Control and Prevention found that the number of new infections in black gay and bisexual men 13 to 29 years old is approximately twice that of white or Latino gay men in the same age group.

The AIDS Foundation is also funding a new program to raise awareness about acute infections among transgender women. In San Francisco, the HIV incidence in that population is almost 25 percent.

Cost for both programs is $400,000.

Nationally, there were an estimated 56,300 new HIV infections in 2006, according to the CDC.

In San Francisco, 800 to 1,000 new infections occur annually, a number that has held fairly steady for a decade. Experts point to a host of psychological factors for the new cases, ranging from "prevention fatigue" to a shift in internal risk calculators because HIV is now considered a treatable condition rather than a fatal illness.

Preventing new infections

"The same behavior that led to people getting infected can lead to them unknowingly infecting someone else when they have a high viral load," Gibson said. "We've been talking about the San Francisco model of AIDS care for 25 years. We're still trying things first here - we're using technology to find out who is at greatest risk."

San Francisco resident Rick Edwards, 51, underwent the special screening last month before the program officially launched. He learned that he is HIV-negative.

"I look at it as another health tool to protect myself and others," said Edwards, who works as a telecommunications project manager. "It's vitally important to stop the virus from being transmitted. If the results are negative, you can put it all to rest and move on with your life. The test takes away the pins and needles of being concerned."